I have three identical toilets installed in my house. Two work fine but one has been giving me trouble for some time now. It does not flash properly. At the begining of the flash cycle large air bubles come out of the jet outlet (the small hole opposite to the drain hole) after which water goes down well and fast unfortunately usually not taking everything down with it. The only difference between working of this unit and the other two are the large bubbles at the begining of the flash cycle. Any ideas? Toilet type is Gerber K 7 10 965